Get the data from sub collection after filtering the field of collection using where clause and provide it to stream builder – Flutter

This is the code I tried

Stream<QuerySnapshot> _usersStream = FirebaseFirestore.instance .collection("ChatRoom") .where("users", arrayContains: Constant.myname) .snapshots(); 
@override

Widget ChatMessageList() { return StreamBuilder(   
 //  stream: chatMessageStream,
    stream: _usersStream,
    builder: (context, AsyncSnapshot<QuerySnapshot> snapshot) {
      if (snapshot.data == null) {
        return Center(
            child: CircularProgressIndicator(
          color: Colors.orange.shade600,
        ));
      } else {
        return Container(
          padding: EdgeInsets.only(top: 15),
          height: MediaQuery.of(context).size.height / 1.2,
          child: ListView.builder(
              itemCount: snapshot.data!.docs.length,
              itemBuilder: (ctx, index) {
                QuerySnapshot<Object?>? snap = snapshot.data; // Snapshot
                List<DocumentSnapshot> items =
                    snap!.docs; // List of Documents
                DocumentSnapshot item = items[index];
                String v = item['chatroomid'];
                return SingleChildScrollView(
                  child: StreamBuilder(
                      stream: FirebaseFirestore.instance
                          .collection("ChatRoom/$v/chats")
                          .orderBy("time", descending: true)
                          .limit(1)
                          .snapshots(),
                      builder: (context, snapshot2) {
                        if (snapshot2.hasData) {
                          QuerySnapshot<Object?>? snap2 =
                              snapshot2.data; // Snapshot
                          List<DocumentSnapshot?>? items2 =
                              snap2?.docs; // List of Documents
                          DocumentSnapshot? item2 = items2?[0];
                          print(item2?['message']);
                          return MessageTile(
                            username: item['chatroomid']
                                .toString()
                                .replaceAll("_", "")
                                .replaceAll(Constant.myname, ""),
                            chatroomid: item['chatroomid'],
                          );
                        } else {
                          return CircularProgressIndicator();
                        }
                      }),
                );
              }),
        );
      }
    });
}

This is the code. One streamBuilder to get the users with where Condition. ListViewBuilder to Display users and second streamBuilder to fetch the last message from the chat sub collection.

But I am facing this issue: